Chronic rheumatoid arthritis (sometimes abbreviated as RA hereinbelow) is an autoimmune disease, wherein inflammation is produced chronically at joints to cause swelling or degeneration due to a cause unknown to date.
It is believed that the inflammation in RA is associated with prostaglandin E (PGE), prostacyclin (PGI), histamine, or kinin such as bradykinin, so that anti-inflammatory agents, typically NSAIDs (nonsteroidal anti-inflammatory drugs), are often prescribed as a first treatment. When such anti-inflammatory agents do not take effect, then antirheumatic drugs are prescribed, such as immunosuppressants that suppress the overall immune function by suppressing inflammatory cytokines, such as TNF-α, interleukin-1 (IL-1), or IL-6, which are involved in immunomodulation via T-lymphocytes or B-lymphocytes, or immunomodulators that suppress only the abnormal immune function relating to RA. Recently, such antirheumatic drugs may sometimes be prescribed even in the initial stage of treatment.
However, antirheumatic drugs, such as the conventional immunosuppressants or immunomodulators, have side effects of some kind, so that prescription for such drugs should be restricted to some extent. In order to suppress the side effects as much as possible, a molecular biological approach which is targeted only to the molecules that exaggerate RA, has recently been made. Biopharmaceuticals have also been under development, utilizing, for example, anti-TNF-α monoclonal antibodies, soluble TNF-α receptor (sTNFR) fusion protein, IL-1 receptor antagonists, or IL-6 receptor antibodies.
On the other hand, there have conventionally been identified various physiological functions of milk components and digestion products thereof. For example, Patent Publication 1 discloses that certain enzymatic digestion products of certain milk protein have a TNF-α or IL-6 inhibitory effect, and may mitigate systemic inflammatory response syndrome or inflammatory responses. Patent Publication 2 discloses that a casein hydrolysate containing free amino acids and peptides which has been obtained by hydrolyzing animal milk casein to have an average chain length of not longer than 2.1 in terms of the number of amino acid residues, has an angiotensin I converting enzyme inhibitory activity and a hypotensive effect.
However, it is not known to date that milk components or digestion products thereof, which are known as a food material and have sufficiently assured safety, have a RA inhibitory effect.    Patent Publication 1: JP-2004-155751-A    Patent Publication 2: WO-2005-102542-A